The base film of a magnetic tape used commonly in video tape recorders contains particles of diameters less than 3 or 4 microns which are provided in order to make the magnetic tape slippery. It is preferable to make the tape as thin as possible, therefore if the diameter of the lubricating particles contained in the coating on the magnetic tape is larger than a predetermined diameter, the tape is considered to be defective. In accordance with the filter apparatus of the present invention, it is possible to provide lubricating particles of uniform diameter which can be used to manufacture defect free magnetic tape.
Conventionally, in the thread manufacturing field, thread or yarn is dyed by blending pigment particles directly into the thread. If the pigment particles to be mixed into the thread are larger than a predetermined diameter, gnarls are formed in the thread and as a result faults occur in the weaving operation of the defective thread by a weaver machine. It is therefore important that the particle diameter of the pigment blended with the thread is uniform. Using the filter apparatus according to the present invention the diameters of pigment particles can be kept consistent so that colored thread free of defects ca be produced.
In the field of fine ceramics, if any coarse particles are contained in the raw material or if foreign particles are absorbed from the environment into the raw material during the manufacture of fine ceramics, they result in defects in the finished products after the baking operation. It is essential therefore to remove all coarse or irregular particles and foreign particles from the raw material of fine caramics. In accordance with the filter apparatus of the present invention, any undesired particles such as coarse or foreign particles can be eliminated from the raw material and, thanks to the purity of the raw material, fine ceramics free of defects can be producted.
Thus, the filter apparatus of the present invention is useful for filtering undesired particles from various types of slurry so as to obtain slurry containing only particles which are less than a predetermined diameter.
Another favorable aspect of the filter apparatus, according to the invention is its capacity to disperse or distribute particles in a slurry. The dispersive function makes the invention particularly useful in the refining process for fuel oil, in addition to the various industrial fields mentioned above. For example, C-class heavy oil used commonly as ship fuel oil contains a large percentage of sludge residue. The sludge residue contains various substances such as catalysts and high molecular substances. Therefore before C-class heavy oil is used as a fuel for a diesel engine the useless elements of the sludge must be removed. The high molecular substances contained in the sludge can be used as a fuel if the particles of the substance are well distributed. The high molecular substances, however, tend to clog filter elements making it difficult to strain sludge to obtain the high molecular substances by means of conventional filter systems. In accordance with the filter apparatus of the present invention, dispersion and filtering operations are simultaneously carried out making the filtering operation extremely efficient.
A filter apparatus manufactured by the applicants of the present invention under the name fujimicro sonic filter carries out a continuous filtering operation during which material caked onto the surface of the filter element is continuously removed. In this filter apparatus, there are an exterior chamber and an interior chamber which are separated from each other by cylindrical filter. The exterior chamber has an inlet and the interior chamber has an outlet. Layers of material caked onto the filter element of the filter apparatus are continuously broken up with ultrasonic waves during the filtering operation.
FIGS. 2 and 3 give a side elevation cross sectional view and a cross sectional plan view of the above prior art filter apparatus, in which caked layers of material are continuously broken up by means of ultrasonic waves. As shown in FIG. 3, slurry is introduced through an inlet 30 and discharged from an outlet 32 after it is filtered through a filter 31. During the filtering operation, the coarse particles contained in the slurry form a layer on the surface of the filter element. Ultrasonic waves are directed onto the layer of material on the filter from a horn 34 connected to an ultrasonic wave generator 33, whereby coarse particles are dispersed, thus removing the caked layer. Because the cylindrical filter continuously rotates, the whole surface of the filter is cleaned by ultrasonic waves in successive portions. In order for the filter apparatus to operate properly, it is necessary that the particles are dispersed by the ultrasonic waves at a rate that is equal to, or better which exceeds, the rate at which the particles accumulate on the filter surface.
The dispersing and filtering capacity of the apparatus is determined by various factors relating to the amplitude of ultrasonic waves, the shape of the horn, the distance between the front end of the horn and the filter element, the pressure of liquid to be treated, and the rotation speed of the filter. The cohering particle volume is determined by the particle density of the liquid, particle diameter, and mesh size of the filter. Although the above type of filter apparatus using ultrasonic waves has considerable filter capacity, the conventional filter apparatus is still sometimes insufficient to filter slurry having high particle density.
The general purpose of the present invention is to provide a high efficiency filter apparatus capable of carrying out a continuous filtering operation for slurries containing hard fine particles and/or having high particle density.